Electrosurgery includes the use of electrical energy in the form of alternating current at radio frequency (RF) levels to cut and/or coagulate biological tissue. The RF energy is typically produced by electrosurgical generators and applied to the tissue via electrodes that are electrically connected to the generator. The art of electrosurgical generators is well known. A variety of types of conventional electrodes have been employed for various types of electrosurgery in a variety of types of applications.
The use of conventional electrosurgical electrodes, however, is problematic in certain respects. For example, many electrosurgical electrodes cause arcing of electrical current between the electrode tip and the underlying tissue, rather than delivering the current in a uniform manner. Arcing may cause excessive tissue damage due to the large amount and density of the electrical energy transferred to the tissue via the arc of current. In addition, arcing causes conventional electrodes to develop hot spots at the point on the surface of the electrode where the arc contacts the electrode. These hot spots cause problems when they contact the tissue, because the tissue tends to stick to the hot spot. When the electrode is then moved or manipulated in any manner, the stuck portion of the tissue is pulled away from the surrounding tissue, causing further damage. Such sticking of the tissue to the electrode is a commonplace problem in surgery. This problem can be especially detrimental in precise surgical procedures. In particular, plastic, neurological, and gynecological surgical procedures are areas where sticking can often be harmful to patient outcome.
In order to reduce this sticking characteristic, electrodes with non-stick coatings have been developed. Unfortunately, the success of these coatings has been limited. Non-stick coatings of materials such as fluorinated hydrocarbon, silicon, and carbon have been used to coat the portion of the electrode that contacts the tissue. Such coatings are discussed in U.S. Pat. Nos. 4,785,807, 4,333,467 and 4,074,718, respectively. One problem with such coatings is the eventual breakdown of the coating over time due to the RF current flowing therethrough. Of course, once the coating detiorates, the non-stick characteristics do as well.
Materials with higher thermal conductivity, such as copper or copper alloys have also been used to reduce the sticking of tissue to electrodes. This is disclosed in U.S. Pat. Nos. 4,492,231 and 5,423,814. Copper, however, is not biocompatible, thus electrodes made of this material are not viable for medical use. Additionally, forceps with nickel tips have been used with some success to reduce sticking. This invention is disclosed in U.S. Pat. No. 5,196,009. While nickel is biocompatible and has a slightly higher thermal conductivity than stainless steel, which is traditionally used for forcep tips, sticking to nickel-tipped forceps still occurs.
It would therefore be desirable to provide improved electrode tips for use in electrosurgical techniques. Such electrode tips should be capable of applying radio-frequency energy evenly and uniformly to the tissue, without significant arcing or charring. In particular, the electrode tips should apply the radio-frequency energy without sticking so that damage to the tissue does not occur. The electrode tips should be usable with conventional electrosurgical power supplies and should have geometries which permit both accessibility to the patient target sites as well as providing the proper energy density and flux for performing coagulation and other conventional electrosurgical procedures.
In recent times, a split has developed between the medical communities in Europe and the United States. The desire to reduce the cost of medical supplies and, thus, medical procedures causes a portion of the medical community to embrace reusable medical supplies and instruments. Typically such items are sterilized with an autoclave, ethylene oxide gas, or other suitable technique, before re-use. Such reusable items must be able to withstand repeated sterilization through the autoclaving or other sterilization processes. In addition, reusable items need to be designed to withstand the wear and tear of repeated use. On the other hand, another portion of the medical community avoids reusable materials in order to reduce the likelihood of contaminating patients and medical personnel. In order to reduce such contamination, disposable items are used predominantly, or at least portions of the instruments and supplies are disposable. Some of the other reasons supporting reusables are that more expensive materials can be used in reusable supplies and instruments, when those more expensive materials have desirable characteristics, and also that the environmental impact of disposable items is so great.
U.S. Pat. No. 4,074,718 discloses an electrosurgical instrument with electrodes of increased thermal conductivity and a plurality of heat radiators attached thereto. Unfortunately, this reference did not recognize the importance of using bio-compatible materials, as several bio-compatible materials (silver and gold) were mentioned as interchangeable with non-compatible materials such as copper, aluminum, and beryllium. As to bio-compatibility at least, these materials are clearly not interchangeable, and they are probably not interchangeable in many other regards as well. In addition, the heat radiators on the electrode are poorly conceived, having a different effectiveness at different positional attitudes. Since the radiators rely on natural convection to remove heat from the electrode, the heat radiators will not function well when the electrode is oriented primarily vertically because the heat radiators will then be positioned above each other and heat convection away from the radiators will not easily occur. In addition, the embodiment with the ball electrode, shown in FIGS. 3 and 4 of this reference, will not conduct heat effectively to the radiators since there will be a bottleneck in the smaller diameter region between the ball and the heat radiators. Similarly, the embodiment shown in FIGS. 1 and 2 of this reference will not conduct heat effectively to the heat radiators because the electrode is a blade electrode having a relatively small cross-sectional area relative to its length which restricts the heat flow.
U.S. Pat. No. 5,423,814 discloses a bipolar coagulation device intended for endoscopic applications. While there is a discussion in this reference of the need to use metals having high thermal conductivity for the electrode materials, the disclosure is of an alloy of such materials, namely an alloy comprised roughly of 80% copper, 15% silver and 5% phosphorous. Unfortunately copper is not bio-compatible, and it is believed that phosphorous is not as well. A particular electrode shape intended to enhance heat transfer away from the electrode tip to reduce tissue sticking is disclosed in FIG. 9a of this reference. The conical shape disclosed may suffer from the drawback that there may be no adequate heat reservoir toward which to transfer the heat away from the tip. In addition the width of the conical shape near the tip will reduce the surgeon's visibility. It is desirable that the electrode block the surgeon's view of the surgical site as little as possible.
It has generally been believed by those in the medical industry that silver, while high in thermal conductivity, is not bio-compatible. Apparently this belief arose because people referring to silver usually, if not always, are referring to sterling silver. Sterling silver is an alloy composed of 92.5% silver and 7.5% copper. Since copper is clearly not bio-compatible, testing of sterling silver has shown it is not bio-compatible. In addition, pure silver is almost never used in any applications since it is so soft or ductile. This is one reason why sterling silver is used rather than pure silver. In addition, pure (or nearly pure) silver is not commonly available through supply channels.
It is against this background, and the desire to solve the problems of the prior art, that the present invention has been developed.